Stabilized isoolefin polyolefin interpolymer derivatives and method of producing same



United States Patent STABILIZED IsooLEFIN roLYoLEFIN INTER- POLYMERDERIVATIVES AND METHOD OF PRODUCING SAME RichardT. Morrissey, Cuyahoga-Falls, Ohio, and Henry J. Weiss, Joliet, Ill., assiguors to The B. F.Goodrich SCfonlipany, New York, N. Y., a corporation of New No Drawing.Application October 29, I953 Serial No.389-,143

3 Claims. (Cl. 260-235) as isobutylene and a minor proportion of one ormore polyolefins (that is, diolefins, triolefins or other olefinscontaining more than one double bond), which interpolymers arecharacterized by high molecular weight, low unsaturation and reactivity(vulcanization or curing) with sulfur to yield an elastic product. Suchinterpolymers are described in U. S. patents including Nos. 2,322,073;2,356,128; 2,356,129; 2,356,130; 2,373,706; 2,384,975; 2,418,912 and2,568,656 and 2,628,955. The presently best known examples of suchinterpolymers are the copolymers of isobutylene with a small proportionof isoprene or butadiene known to the rubber industry as Butyl (or GR-I)rubber.

While Butyl rubber has found considerable use in the manufacture ofinner tubes, it possesses inherent disadvantages which have preventedits more widespread use. It vulcanizes or cures more slowly than otherWidely used sulfur-vulcanizable rubbery materials, it does not adherewell to other materials including natural rubber,

. and when it is mixed with natural rubber andthemixture vulcanized theresultingvulcanizates are generally less valuable than vulcauizates fromeither of the rubbery materials alone.

It is disclosed in U. S. Patent 2,631,984 that the introduction ofbromine atoms into the polymer structure of Butyl rubber and similariso'oIefin-polyolefin interpolymers, so as to produce units of thestructure Br Br 1 as by bromination of such interpolyme'rs', results innew materials with properties unexpectedly superior to those of thebromine-free materials. Such brominated rubbery isoolefin-polyolefininterpolymers cure or vulcanize quite rapidly even with vulcanizingagents which are totally ineffective with the unbrorninated materials,to yield vulcanized products which far surpass those obtained from theunbrominated materials in a number of respects. In addition, thebromin'ated interpolymers, unlike the un- 2,833,734 Patented May 6,1958

brominated materials, adhere well to a wide variety of materialsincluding metals, plastics, and natural and synthetic rubbers. They are,therefore, of considerable value as adhesives. They may also be mixedwith natural rubber or any of the various known butadiene syntheticrubbers in any desired proportions and. theresulting mixturesco-vulcanized to give products' of excellent properties.

It has been'found, however, that therubberybrominated isoolefinpolyolefin interpolymers are per so somewhat unstable as evidenced bytheir development of color upon heat aging or upon long standing at roomtemperature and by'their becoming progressively tougher during storageorheat aging or during the Mooney viscosity determination. Their lack ofstability also sometimes results in progressive. degradation oftheirvulcani'zates,

during extended exposure to heat, in such physical and chemical.properties as tensile, strength, elongation, modulus, flex-life, ozoneresistance, andadhesiveness; The copend'ing application of Richard A,Crawford and Richard TfM'orrissey, Serial No. 308,167, filed Septem bet"5, 1952, now U. S. Patent 2,681,899, discloses that certain metalsilicates are stabilizers for: bromin'at'ed isoolefinpolyolefininterpolymers.

The invention of this application resides in thetdiscover-y that suchbrominated isoolefin polyolefirr interpolymers may be efficientlystabilized against such nudesirable changes by incorporating therein asmall amount of an epoxidized fatty acid ester of a class tobe1hereinafter defined. The resulting stabilized composition has theproperties of the original brominated interpolymer and in addition issufiiciently stable to withstand. prolonged storage-and exposure to heatand light and other deleterious influences. Vulcanizates. prepared fromthe stabilizer-containing compositionsare likewise. of superiorstability to heat.

The epoxidized fatty acid esters of this inventionare preferably epoxyoleic and linoleic acid. esters. A useful product for the purposes ofthis invention is obtained, for example, by epoxidizing cotton seed oilwhich contains oleic and linoleic glycerides. Other usefulfattyacidesters include esters of unsaturated linolenic', elaeostearic,

'ricinoleic and like acids with alcohols, diols, triols, and

carbon-to-carbon double bond. The estersQand polyesters of the fattyacids include. esters of the aliphatic alcohols containing more thanthree carbon atoms,sand preferably from 5 to 10 carbon atoms, polyhydricalcohols such as the diols containing 2 to 10 carbon atoms representedby ethylene glycol, butanediol, tetraethylene glycol, diethylene glycoland the like, and triols such as glycerin and the like. A convenientsource of the fatty acid esters are the naturally occurring unsaturatedoils such as the vegetable oils: cotton seed, castor olive, peanut,corn, soya, rung, linseed and the like; fish oil's; animal fats and thelike, These oils ordinarily contain oleic, linoleic, linolenic, and/orelaeostearic acid esters. The epoxidized fatty acid esters may beprepared, for

as described in'U, S. Patent 2,567,930, or the method of U. S. Patent2,485,160 whereby the epoxidatibn reaction is carried out by treatingthe ester with a mixture brominated interpolymer.

the stabilizer thereto.

weight based on the rubbery interpolymer.

of hydrogen peroxide and formic acid. In any event the unsaturatedcarbon-to-carbon double bond is changed to an epoxy group as one epoxygroup for 2 molecules of the acid, or there maybe three epoxy groups permolecule of acid since linolenic acid contains three unsaturated doublebond groups. The preferred epoxy fatty acid esters for use in thepractice of this invention are esters of oleic and linoleic acid .withglycerol, glycols containing 2 to 4 carbons atoms and aliphatic alcoholscontaining 5 to carbon atoms, said epoxidized fatty acid ester tocontain at least A. mol of epoxy group per mol of fatty. acid.

The epoxidized fatty acid ester stabilizer may be incorporated into thebrominated interpolymer at any time before vulcanization although it ispreferred to incorporate the stabilizer as an integral step inmanufacture of the If incorporated into the solid brominatedinterpolymer, this may be done satisfactorily on a two-roll rubber millor in a Banbury or other internal mixer or by dissolving or dispersingthe brominated interpolymer in an appropriate medium and adding Thepreferred method is to blend the stabilizer with a solution containingthe brominated interpolymer as obtained from'the bromination process andto effect coprecipitation of thebrominated interpolymer and thestabilizer in the form of discrete particles in which the latter isuniformly dispersed in the former. The exact manner in which thepreferred incorporation step is carried out will be more fully describedbelow.

Theamount of the epoxidized fatty acid ester stabilizer requiredforefficient stabilization will vary somewhat depending on the interpolymertreated and on its brominecontent, on the epoxidized fatty acid esterutilized and on its compatability with the rubber. In general,significant stabilization is noted, in amounts as little as 0.5 to 1% byThe beneficial effect increases withincreasing amounts of stabilizer upto about. 20%. For stabilization only, however, amounts of l or 2 to 5%are preferred. Amounts up to to volumes or more .of stabilizing per 100volumes of bromine-containing interpolymer or from 1 to 100% by weightor more may be utilized.

The brominated isoolefin-polyolefin interpolymers in which thestabilizer is incorporated are prepared, according to a preferredprocedure described in U. S. Patent No. 2,631,984 by reacting a rubberyisoolefin polyolefin hydrocarbon interpolymer with a brominating agent,preferably in solution. Since the reaction which occurs involves anaddition of bromine to olefinic double bonds, the isoolefin polyolefininterpolymer used must and will, of course, contain olefinicunsaturation, but its nature may otherwise be varied widely.

Preferred isoolefin polyolefin interpolymers for use in preparingbrominated derivatives .are the solid, plastic rubbery .interpolymers(in other words, high molecular weight polymers) of a major proportion,more desirably from 70 to 99% by weight, of an isoolefin generallycontaimng from 4 to 8 carbon atoms and a terminal methylene group, suchas, most desirably, isobutylene or, alternatively, 3-methyl butene-l,4-methyl pentene-l, Z-ethyl butene-l, 4-ethylpentene-1, 4-ethylhexene-1or the like, or a .mixture of such isoolefins, with a minor proportion,des1rablyfrom 1 to by weight, of a polyolefinic hydro- 4 carbongenerally containing from 4 to 18 carbon atoms, or two, three or moresuch polyolefinic hydrocarbons, including the following:

(1) Acyclic diolefins or open-chain, aliphatic conjugated dienes such asbutadiene-1,3, isoprene, 2,4-dimethyl butadiene-1,3, piperylene,3-methyl pentadiene-1,3, hexacliche-2,4, 2-neopentyl-butadiene-l,3 andthe like;

(2) Acyclic non-conjugated diolefins such as dimethallyl and itshomologs containing 2 to 6 carbon atoms inter-- posed between twoisopropenyl radicals, Z-methyl hexadiene-l,5, Z-methyl pentadiene-1,4,2-methyl heptadiene- 1,6, Z-methyl heptadiene-1,4 and other tertiarynonconjugated diolefins having one double bond in the termi-' nalposition attached to a tertiary carbon atom;

(3) Alicyclic diolefins, both conjugated and non-conjugated, such ascyclopentadiene, cyclohexadiene, l-vinyl cyclohexene-3 l-vinylcyclohexene-l, 'l-vinyl cyclopentene-l, l-vinyl cyclobutene-2,dicyclopentadiene and the.

like as well as monocyclic diolefinic terpenes such as dipentene,terpinenes, terpinolene, phellandrenes, syslvestrene and the like;

(4) Acyclic triolefins such as 2,6-dimethyl-4-methylene' heptadiene-2,5,2-methyl hexatriene-l,3,5 and other conjugated triolefins, as .well asmyrcene, ocimene, alloocimene and the like; t

(5) Alicyclic triolefins such as fulvene, 6,6-dimethyl fulvene,6,6-methyl-ethyl fulvene, 6-ethyl fulvene, 6,6- diphenyl fulvene,6-phenyl fulvene and other fulvenes of the formula V 1 where R ishydrogen, alkyl, cycloalkyl, or aryl; as well as other alicyclictriolefins such as 1,3,3-trimethyl-6-vinyl cyclohexadiene 2,4,cycloheptatriene, etc.;

(6) Higher polyolefins such as 6,6-vinyl methyl fulvene (a tetraolefin)and 6,6-diisopropenyl fulvene (a pentaolefin), and

(7) Aromatic hydrocarbons containing a plurality of olefinicallyunsaturated non-aromatic hydrocarbon groups such as vinyl groups,representative of which are divinyl benzene and similar polyvinyl orpolyisopropenyl aro' matic hydrocarbons.

Such solid, plastic, rubbery interpolymers, for use in preparingbrominated derivatives, are themselves generally prepared by lowtemperature polymerization (from 0" to C.) utilizing an appropriatecatalyst, generally an active metal halide or Friede-l-Crafts typecatalyst such as aluminum chloride or boron trifiuoride, dissolved in alow freezing solvent such as methyl or ethyl chloride, and, when soprepared, generally possess an average mo- ,lecular weight above 15,000and as high as 30,000 to 200,000 or higher, iodine numbers in the range0.5 to 50,

and are reactive with sulfur to yield elastic products. Most importantof these are the solid plastic interpolymers of isobutylene with smallamounts of isoprene or butadiene, of the type known as Butyl or GR-Irubber.

However, it is to be understood that the epoxidized fatty acid esterstabilizers are equally effective when applied to brominatedinterpolymers made fromisolefin polyolefin interpolymers other than thepreferred materials set forth above. Any of the known isoolefinpolyolefin hydrocarbon interpolymers may be converted to usefulbrominated derivatives and utilized in the method of this invention. Forexample, resinous interpolymers of low molecular weight and/ or notreadily vulcanizable with sulfur are readily converted to brominatedderivatives having enhanced adhesive properties and the ability to beutilized advantageously in the compounding of rubbery materials.Similarly, isoolefin polyolefin hydrocarbon interpolymers containingother interpolymerized monomers such as styrene, chlorostyrenes, acrylylchloride,

methallylchloride, and other monoolefi'nic monomersfalso areadvantageously utilized to :pr'epare'bromina'ted, derivatives. Toillustrate, a brominated'interpolymer of 50 percentisobutylene, 30percent'styrene and 20 percent isoprene is superior to the correspondingunbrominated interpolymer as an adhesive and in the compounding ofrubbery materials. v i t In preparing the brominated' derivatives forusein this invention, any brominating agentmay beutilized such asmolecular bromine itself or the:compounds of bromine :which liberatemolecular bromine among which are sodium hypobromite, magnesium bromidehexahydrate, N-bromo-succinimide, alpha-bromo acetoacetanilide,betabromoethyl 'phthalimide, N-bromoacetamide, tribromo phenol bromide,bromo-beta-naphthol, pyridinium bromide perbromide, etc.

In accordance with the disclosure of U. S. Patent No. 2,631,984 thebromination may be carried out in many ways. One method consists inpreparing a solution, dispersion or cement of the interpolymer in anappropriate normally liquid organic solvent or diluent such as ahydrocarbon or halogenated derivative thereof (examples of which aretoluene; chlorobenzene, hexane, heptane, trichloroethane, carbontetrachloride, etc.) and adding the brominating agent either as such orin solution, for example, in carbon tetrachloride, to the resultinginterpolymersolution, dispersionor cement thereby to form the brominatedinterpolymer in solution or dispersion in the solvent or diluent. Theresulting solution or. dispersion may be utilized as such, as forexample, when the brominated derivative is employe'cl'as an adhesive, orit may be admixed with a non-solvent for the brominated derivative (suchas alcohol or water) to precipitate the brominated, derivative. whichis, then recovered. in the solid, finely-divided or crumb-like form,ineither of which cases it is preferred that thestabilizerbeincorporatedin the solution or dispersion of brominated interpolymer beforeutilizing the latter as an adhesive or before precipitation thereof; q If A more preferred method, particularly advantageous to those havingButyl type polymerization equipment consists in utilizing as the solventor diluent for the bromination a saturated hydrocarbon orhalogenatedderivative thereof which boils below roomtemperature such as butane,methyl or ethyl chloride, and carrying out the bromination at atemperature and pressure such that the solvent is maintained in theliquid state. .This greatly simplifies recovery of the solvent ordiluent-since the resulting solution of brominated interpolymer can berun into water above theboiling 'poizntof the solvent ordiluent so thatthe latter is flashed-01f and condensed while the brominatedi-nterpolymer is precipitated or coagulated in. a conveniently handledcrumb-like form. The

ethyl chloride solution of interpolymer utilized in thisvariation of theprocess is conveniently prepared by dissolving the solid interpolymer inthe solvent. Preferably, the ethyl chloride solution resulting from theButyl type polymerization may be utilized directly with additiontheretofof a .solution of bromine in ethyl. chloride or carbontetrachloride followed by quenching with an nating reaction occurs quiterapidly and essentially involves the addition of bromine to theoletinicdouble;

Still another method,

agent decomposes to'liberate molecular bonds of the interpolymer-Consequently, the. resulting bromine-containing interpolymers possess intheir structure units of the formula $45.. i. it.

These units, not found in known isoolefin polyolefin hydrocarboninterpolymers, may well be responsible, at least in part, for the uniqueproperties of the bromine-containing interpolymers. It should be pointedout, however, that some substitution may and probably does occur, alongwith addition of bromine to, olefinic double bonds, during thebromination reaction, and that, therefore it is not essential that allcombined bromine be present in bromine.

The brominated interpolymers resulting from the bromination reaction maycontain from aslittle as 0.5 percent by. weight or' 4, 8, 10 or even 15percent by weight, or even as much as 50 percent by weight of combinedbromine depending on the degree of unsaturation of the parentinterpolymer, which in turn depends upon the proportion of combinedpolyolefin in the interpolymer utilized. Preferably, for any givenderivative, .the. percentage of combined bromine is less than that whichwould theoretically be present if all the olefinic C=C units) doublebonds were completely brominated to give: i

and preferably, for high molecular weight rubbery-"isoolefin polyolefininterpolymershaving an iodine number less than 50', that is of thenature of butyl rubber, the percentage of combined bromine is from 20 topercent of the possible theoretical amount. Still more preferably, thepercentage of combined bromine in suchinterpolymers is in the range of 1to 8 percent by weight, and ,for

adhesive applications is in the range of 1.5 to 4 percent by weight.Most useful brominated interpolymers are those derived from butyl rubberin which thepercentage of combined bromine is 40 to 60 percent of.theoretical or 2.5 to 4.5 percent by weight. or, more particularly,about 3 percent by weight.

From the foregoing, it is apparent that the-preferred brominated'interpolymer derivatives for use-in this invention are not completelysaturated: but that they are less unsaturated than the parentunbrominated interpolymers. Their molecular weights are not preciselyknown,

but they are of the same order as the parent interpolymer.

Even though some depolymerization nrayo'ccur during bromination theirapparent molecular weights are generally about the same or slightlyhigher because of the presence of the relatively heavy bromine atoms.

Bromination of isoolefin polyolefin interpolymers so as to produce dimastructure.

a not'the only-method of arriving at interpolymers con- "tainih gsuchunits, butis at present preferred. Another method consists ininterpolymerizing an isoolefinic monomer with a polyolefinic monomer atleast one of wluch monomers is brominated so' as to contain the I t BrBr For example, the interpolymerization of isobutylene with2,3-dibromo-butadiene-1,3--which has the unit in its structure ofCHFCC=CH2 Br I Br results in the production of an interpolymercontaining such units; this interpolyme'r, however, is more unsaturatedfor a given bromine content than are the brominec'ontaininginterpolymers produced by the bromination of isoolefin diolefininterpolymers.

' \As mentionedabove, the bromine-containing isoole- 'fin polyolefininterpolymers are possessed of unique propproducts, in whichtheunbrominated isoolefin polyolefin interpolymers are not entirelysatisfactory. For example, the stabilized brominated interpolymers ofthis invention, without further addition of compounding ingredients, areexcellent adhesives to bond rubbery materials to each other or to metaland other structural materials, being especially useful in bonding theunbrominated isoolefin polyolefin interpolymers to each other, tonatural rubber and to diene synthetic rubbers. The stabilizedbrominecontaining interpolymers are compatible in all proportions withthe natural and diene synthetic rubbers forming vulcanizable admixturestherewith which possess the desirable properties of remarkably increasedozone resistance, improved resistance to flexing, and increasedresistance to airditfusion. In any of these uses they may be compoundedwith any of the conventional ingredients used in compounding theunbrominated rubbery isoolefin polyolefin interpolymers or other rubberymaterials, and they may be vulcanized by the same general methods. Theirvulcanization proceeds much more rapidlythau that of the unbrominatedmaterials, despite their generally lower degree of unsaturation, andthey may be vulcanized in the absence of sulfur with agents, such as thepolyvalent metal oxides particularly zincoxide, which are ineffective invulcanizing the parent unbrominated interpolymer.

The preparation of representative bromine-containing interpolymers andtheir stabilization according to this invention are more fully set forthin the following examples which are illustrative only since numerousvariations and modifications therein will be apparent to those skilledin the art. In the examples, all parts, unless otherwise indicated, areby weight.

EXAMPLE 1 91 parts of a solid plastic rubbery copolymer of about 97percentisobutylene and 3 percent isoprene known as Butyl or GR-L? isdissolved in sufficient n-heptane to form a fluid solution, 9 parts ofliquid bromine as a 10 percent solution in carbon tetrachloride are thenadded to the heptane solution and the resulting mixture stirred forabout one hour in the dark. An excess of sodium carbonate as a 10 topercent solution in water is then added to neutralize the unreactedbromine. After a short period of agitation the neutralized brominatedcement is blended with a quantity of methanol to precipitate thebrominated copolymer, the latter then being filtered, washed and dried.The brominated copolymer thus obtained contains 2.25 percent of combinedbromine and is slightly softer than the parent copolymer.

The copolymer when vulcanized by sulfur either alone or in blends withnatural rubber or with butadiene-styrene or butadiene-acrylonitrilesynthetic rubber forms strong, highly useful compositions. However, whenthe raw brominated copolymer is allowed to stand in air content-andMooney viscosity at 1 minute, 10 minutes, and 20 minutes using the 1.2inch rotor at 250 F.:

t Bromine Mooney Viscosity Days Aged at 70 0. Content,

Percent M1 M 10' M 20' 2. 25 63 7s 81 2.18 as 104 104 2. 04 110 120 1122.23 128 115 110 The physical properties of vulcanizates of thebrominated copolymer also deteriorate during aging at 70 C., the tensilestrength of a sulfur vulcanizate of an unaged sample of brominatedcopolymer in a 60/40 blend with natural rubber being 1775 lbs. persquare inch, while that of a similar blend containing a brominatedcopolymer aged 3 days at 70 C. is considerably less.

The unstabilized brominated copolymer also increases in Mooney viscosityduring a Mooney viscosity determination. After an initial reading of 21,a stock containing such copolymer evidencesa Mooney viscosity of 37after 1 minute and .47 after 15 minutes at 250 F. When aged for sevendays at 70 C. the same stock is of a dark color and evidences an initialMooney reading of 51, a 1 minute Mooney of 76 and a 15 minute'Mooney of72.5. By contrast when only 1.25 percent, based on the brominatedcopolymer, of an epoxidized cotton seed form a white sidewall tirecompound as follows:

' Parts by weight Brominated copolymer 60.0 Natural rubber 40.0

Zinc oxide 87.0 Ultramarine Blue 0.2 Titanium dioxide 14.0 i I Stearicacid 1.5 Mercaptobenzothiazole 0.75 Di-orthotolyl guanidine 0.25 Sulfur2.50

oil which is a glyceride of oleic and linoleic acids and which containsabout one epoxide group per mol of acid is milled into the brominatedcopolymer,'the resulting composition is light in color, has a 1 minuteMooney of 36 and a 15 minute Mooney of 20. After aging for seven days atC. the stock is a very light butt in color and has a 1 minute Mooney of38. Thus, only 1.25 percent of the epoxidized fatty acid ester issutficient to stabilize the brominated copolymer during processing andto prevent blackening of the stock, not only during processing but alsoduring an accelerated 7 day heat aging.

The incorporation of an epoxidized fatty acid ester into the brominatedisoolefin polyolefin interpolymer not only stabilizes the latter againstheat-induced changes in plasticity and color during processing andstorage but also a has a very beneficial effect on the physicalproperties of vulcanized compositions prepared therefrom. Separatesamples of the unstabilized brominated copolymer described above, bothaged and imaged, and an aged sample of the stabilizer compositioncontaining 1.25 percent epoxidized fatty acid ester are compounded withnatural rubber and the usual sulfur vulcanization ingredients to assentWhen portions of each c'ompo'sitionarfe" vulcanized at 280 F. forvarying periods of time the physical properties of the vulcanizates areas shown in the following Table I:

results are obt ined when polymer containing 5.0 parts er stabilizer areemployed.

, EXAMPLE III A brominated copolymer of the type shown in ExampleInspection of the data in Table I clearly shows that without stabilizer,aging for 7 days in air at 70 C. results in a lowering of the physicalproperties of the white side EXAMPLE II The isobutylene-isoprenecopolymer utilized in the bromination step of Example I is dissolved inliquid ethyl chloride to form a percent solution containing 100 parts ofcopolymer. A solution containing 5 to 16 parts of bromine dissolved inethyl chloride is added to the copolymer in a closed vessel and theresulting mixture stirred for five minutes at which point an excess ofalcoholic potassium hydroxide is added to neutralize the unreactedbromine. After stirring for several minutes to allow neutralization tobe completed, an ethyl chloride solution of epoxidized cottonseed oil (2percent based on the weight of brominated copolymer) is added and themixture stirred rapidly. Following further stirringto form asubstantially homogeneous mixture the contents of the reaction vesselare discharged in a fine stream or spray into a closed coagulating tankfitted with a condenser and containing hot water (60-70 C.) and acolloidal dispersing agent of zinc stearate, whereupon the ethylchloride is flashed off and condensed and the brominated copolymer isobtained as a fine crumb-like coagulum. The presence of zinc stearate inthe copolymer solution and in the coagulation bath assists in obtaininga fine, small sized and non-sticky crumb. The coagulum is finallyseparated by filtering and is washed once or twice with clear water anddried.

The brominated isobutylene-isoprene copolymer containing the epoxidizedfatty acid ester thus obtained contains from 1.5 to 6.0 percent ofcombined bromine (depending on the original amount of bromine used) andis a plastic, easily worked rubbery material having approximately thesame Mooney viscosity as the parent copolymer. compounded with sulfurand accelerators in the natural rubber white sidewall tire compoundof'Example I and then vulcanized, the copolymer derivative contain- Whenexposed to 27.9

After aging the copolymer derivative in air for bilizer cracks in lessthan 100 hours. Similar excellent II is stabilized with 10 part of anepoxidized oleic acid ester of n-hexanol which contains about 1.0 epoxygroup per mol of acid. This polymer is then compounded in the recipe ofExample I and tested both before and after aging. The unaged examplecured for 20 minutes at 292 F. has a tensile strength of 2725 pounds persquare inch and an elongation of 525 percent. After aging 16 days at 70F. .the stabilized polymer has a tensile strength of 2500 pounds persquare inch and an elongation of 425 percent demonstrating theoutstanding stabilizing properties of this epoxidized fatty acid ester.

EXAMPLE IV The previous examples have shown the effect of the epoxidizedfatty acid ester stabilizers on 60/40 blends of the brominated isoolefinpolyolefin polymers with natural rubber. Blends with natural rubberranging from 5 to percent of the bromine-containing polymer and 5 to 95percent of natural rubber or natural rubber reclaim also are sostabilized. Similar stabilization effects are noted also in vulcanizatesprepared from the brominecontaining polymers alone and in blends withother natural and synthetic rubbers and reclaimed forms .of suchrubbers. Specifically, blends ranging from 10 to 95 percent by weight ofthe bromine-containing isoolefin polyolefin polymer and 5 to 95 percentof butadiene acrylonitrile copolymer rubbers are similarly stabilizedagainst discoloration in the raw polymer state and in the form ofsulfur-vulcanizates are stabilized during heat-aging and are possessedof better hot-flexing and hot tensile properties. Also similar blendswith butadiene styrene copolymer rubbers, polychl'oroprene rubbers,unbrominated Butyl rubbers, Thioko l-type rubbers and others are alsoefficiently stabilized by the epoxidized fatty acid esters.

EXAMPLE v Other brominated isoolefin polyolefin hydrocarboninterpolymers show a similar response to the incorporation of theepoxidized fatty acid esters of this invention. For example, a copolymerof .90 to 97 percent isobutylene, 1 to 3 percent isoprene and 2 to 5percent 6,6-dimethyl fulvene prepared by polymerization at about l00 C.in ethyl-chloride using aluminum chloride catalyst and having amolecular weight of from 630,000 to 970,000 and an. iodine value" (bythe Wijs 'methcd) of 2.5 to 10 is easily converted to brominatedderivatives containing from 2 to 7 percent or more bromine. From 1 to 10percent or more or" the stabilizers protect this type of brominatedcopolymer in the same manner as is shown in the foregoing examples.

polyolefin hydrocarbon interpolymers easily converted Still otherisoolefin to brominated derivatives and stabilized by the stabilizers ofthis invention are interpolymers of isobutylene or anand widely usefulclass of materials. It is apparent, therefore, that various embodimentsof the invention, in addi- 1 11. tion 'to'those. specifically disclosed,may be provided without departing from the spirit and scope of theinvention as defined in the appended claims.

We claim:

1. A stabilized rubber composition comprising a partially brominatedderivative of a rubbery interpolymer of from 70 to 99% by weightisobutylene and from 1 to 30% by weight of isoprene, said brominatedderivative retaining residual olefinic unsaturation and containing about1.5 to about 4% by weight combined bromine, and as a stabilizer thereforfrom about 1 to about 5% by weight of an epoxidized vegetable oilcontaining glycerides of oleic and linoleic acids having about 1 molepoxy group per mol of esterified fatty acid in the vegetable oil.

2. The stabilized rubber composition of claim 1 wherein the stabilizeris epoxidized cotton seed oil containing about 1 mol. epoxy group permol of esterified fatty acid in the cotton seed oil.

3. The stabilized rubber composition of claim 2 wherein. the rubberyinterpolymer is an interpolymer of about 97% isobutylene and about 3%isoprene.

References Cited in the file of this patent UNITED STATES PATENTS2,556,145 Niederhauser June 5, 1951 2,590,059 Winkler -2 Mar. 18, 19522,669,549 Darby Feb. 16, 1954 2,720,479 Crawford et a1 Oct. 11, 1955

1. A STABILIZED RUBBER COMPOSITION COMPRISING A PARTIALLY BROMINATEDDERIVATIVE OF A RUBBERY INTERPOLYMER OF FROM 70 TO 99% BY WEIGHTISOBUTYLENE AND FROM 1 TO 30% BY WEIGHT OF ISOPRENE, SAID BROMINATEDDERIVATIVE RETAINING RESIDUAL OLEFINIC UNSATURATION AND CONTAINING ABOUT1.5 TO ABOUT 4% BY WEIGHT COMBINED BROMINE, AND AS AS STABILIZERTHEREFOR FROM ABOUT 1 TO ABOUT 5% BY WEIGHT OF AN EPOXIDIZED VEGETABLEOIL CONTAINING GLYCERIDES OF OLEIC AND LIOLEIC ACIDS HAVING ABOUT 1 MOLEPOXY GROUP PER MOL OF ESTERIFIED FATTY ACID IN THE VEGETABLE OIL.